In a cellular wireless communications system, a radio connection is set up between an Access Terminal (AT) such as a handset and a Base Transmitter Station (BTS), in order to transmit traffic back and forth between them. The traffic can include, without limitation, Voice over IP (VoIP), other voice or audio information, streaming video and digital data in a form such as HTTP or FTP, for use with the Internet. Generally, multiple carriers having a frequency allocation such as 1.25 MHz are used by the same BTS. As used herein, the term “carrier” comprises a carrier pair having a forward link (FL) and a reverse (RL), wherein a forward link carries traffic from the BTS to an AT, and a reverse link conversely carries traffic from an AT to the BTS.
During a radio connection setup it is necessary to select a radio carrier, for use in transmitting a particular traffic flow. Typically, a carrier pair is configured to carry multiple traffic flows. Accordingly, the load on a carrier pair is increased as an increasing number of users start using the carrier pair for both data and voice transmissions. Also, a single user can operate an AT to produce multiple traffic flows, such as one flow for VoIP and another for HTTP data packets.
In view of the substantial and diverse loading that can be placed upon respective carrier pairs of a system, it would be desirable to establish an efficient procedure for assigning newly generated or arriving traffic flows to the carrier pairs. If an arriving flow is assigned to a carrier without considering the current loading levels of available carriers, some carrier pairs might be overloaded while others remain lightly loaded. This can result in underutilization of the over-all system capacity, while at the same time causing congestion and even instability at some of the carrier pairs.
Deficiencies of the above type have characterized previously used techniques for assigning traffic flows to carriers, such as a round robin approach or totally random assignment. In another previous technique, an algorithm was used to assign a flow to a particular carrier based on symmetrical traffic assumptions, that is, on the assumption that the traffic requires the same amount of transmission capacity on both the forward and reverse links. However, this assumption is not valid for certain important classes of traffic flows. For example, HTTP data typically involves an exchange between the user of an AT and an Internet web site, wherein the flow of data is routed through the BTS. Generally, the traffic flow in these situations will be asymmetric, that is, there will be much more traffic through the forward link, from the BTS to the AT, than through the reverse link.